The general results obtained in the previous section are applicable to any stochastic system defined by (REF ) and (REF ). In this section, we particularize these general results for the multiuser communication channel as one of the most important practical stochastic systems. Specifically, we consider the multiple access channel with feedback, which has applications in the cellular networks, medium access in a Local Area Networks (LAN), etc. We first introduce a general model for MAC channel with feedback and then calculate the sensitivity of the mutual information to the channel parameters in this model. These results are particularized to the additive noise MAC and additive Gaussian noise MAC cases. We also explore the counterparts of the results for the MAC without
feedback. The single-user versions of the results are given as well. Finally, we use the obtained results
to interpret the effects of the well-known Schalkwijk–Kailath (S-K) coding
scheme [1]}, on the behavior of mutual information in the MAC with feedback.
